1. Field of the Invention
The present invention relates to a reinforced fire retardant resin composition which is mainly composed of polytetramethylene terephthalate and which possesses improved electrical characteristics.
2. Description of the Prior Art
It is expected that polytetramethylene terephthalate reinforced with glass fibers will be used in a variety of industrial applications because of its balanced properties, especially for use in the fabrication of electrical parts because of its excellent insulating properties. However, such terephthalate materials, especially when they are used in the fabrication of electrical parts, are subject to inflammability problems. It is especially when the polytetramethylene terephthalate materials are used in electrical applications that they should be fire retardant.
Some methods for rendering glass fiber-reinforced polytetramethylene terephthalate materials fire retardant have been proposed. One technique which has been proposed employs various halogen compounds in combination with antimony trioxide as a fire retarder combination.
The combined use of halogen compounds and antimony trioxide has succeeded in imparting a degree of fire retardancy to reinforced polytetramethylene terephthalate. At the same time, however, the electrical characteristics, especially the arc resistance and tracking resistance of the terephthalate materials is an extremely serious problem with these fire retardant materials. Accordingly, an improved method for rendering polytetramethylene terephthalate materials fire retardant is essential.
It has been proposed that the arc resistance of a fire retardant polytetramethylene terephthalate composition reinforced with glass fibers and containing various halogen compounds and antimony compounds as fire retardants can be improved by adding sodium antimonate and talc or boron nitride to the composition. Although the arc resistance of the composition can be improved by the addition of these fire retardant compounds, the tracking resistance can not be sufficiently improved.
Furthermore, the addition of needle-like calcium metasilicate to reinforced polytetramethylene terephthalate materials has also been proposed to improve the arc resistance of polytetramethylene terephthalate. However, in this method, calcium metasilicate must be added to the terephthalate material in an extremely great amount. Moreover, the additive can not be practically used in the compositions which contain a fire retarder. It has also been proposed to add asbestos fibers which have a great L/D to prevent dripping of the terephthalate composition in a flame to retard combustion. However, the fire retardant resin compositions to which asbestos fibers are added cause the formation of black stains on the surface of products molded from the composition which markedly reduces the commercial value of the product. Moreover, the addition of anhydrous silica such as fumed colloidal silica or silicates to terephthalate compositions has also been proposed for the same purpose as the addition of asbestos fibers. These compounds have the effect of preventing dripping of molten material when exposed to a flame. However, the tracking resistance of the composition of the present invention cannot be improved. Thus, no polytetramethylene terephthalate resin composition is currently available which contains a reinforcing filler and which is fire retardant while still retaining the excellent electrical characteristics of polytetramethylene terephthalate, especially the arc resistance and tracking resistance characteristics.